Photonic device structure and fabrication method thereof

ABSTRACT

Various embodiments of a photonic device and fabrication method thereof are provided. In one aspect, a device includes a substrate, a current confinement layer disposed on the substrate, an absorption layer disposed in the current confinement layer, and an electrical contact layer disposed on the absorption layer. The current confinement layer is doped in a pattern and configured to reduce dark current in the device. The photonic device may be a photodiode or a laser.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is the non-provisional application of, and claims thepriority benefit of U.S. Patent Application Nos. 61/796,465, filed onNov. 13, 2012 and entitled “Method for Confining Current Through GeSiPhotonic Devices”, which is herein incorporated by reference in itsentirety.

BACKGROUND

1. Technical Field

The present disclosure relates to photonic devices and, moreparticularly, to confining current in photonic devices.

2. Description of Related Art

Typically the substrate layers in many conventional photonic devices areuniformly and heavily doped in order to reduce series resistance and/orto improve electrical connection, especially for high-speed opticalcommunication applications. As a result, conductive currents can crossthe entire interface between the photonic device and substrate, asillustrated in FIG. 7.

However, not all the conductive currents are useful for deviceoperation, and current from certain region even causes negative impacton device performance of the photonic device. For example, for aphotonic device the useful region is the central region under couplingaperture for normal incident light. Accordingly, those conductivecurrents crossing other regions are regarded as noise that hampersdevice performance. This condition tends to worsen especially when thephotonic device has a large sidewall leakage current. Thus, there is aneed to solve the aforementioned problems.

SUMMARY

In one embodiment, the method may further include forming an opticalbarricade layer that at least partially surrounds the secondsemiconductor structure such that an optical coupling region of thesecond semiconductor structure is covered by the optical barricade layerto avoid the second semiconductor structure receiving the opticalsignal.

In one aspect, a device may include: a substrate; a current confinementlayer disposed on the substrate, the current confinement layer beingdoped in a pattern and configured to reduce dark current in the device;an absorption layer disposed on the current confinement layer; and anelectrical contact layer disposed on the absorption layer and doped withdopants of a first polarity.

In one embodiment, a first portion of the current confinement layer maybe doped with dopants of a second polarity opposite the first polarity,and a second portion of the current confinement layer surrounding thefirst portion may include an intrinsic region.

In one embodiment, the first portion of the current confinement layermay be doped with dopants of the second polarity with a dopingconcentration from about 1×10¹⁶ to about 1×10²⁰/cm³.

In one embodiment, the second portion of the current confinement layermay be doped with dopants of the second polarity with a dopingconcentration has a doping concentration less than 1×10¹⁶/cm³.

In one embodiment, a first primary side of the substrate may include arecess, and the current confinement may be disposed on the first primaryside of the substrate in the recess. In one embodiment, an exposedsurface of the electrical contact layer may be approximately flush witha portion of the first primary side of the substrate that is notrecessed.

In one embodiment, the substrate may be made from a bulk Si wafer asilicon-on-insulator (SOI) wafer.

In one embodiment, a region on a side of the substrate on which thecurrent confinement layer is disposed may be doped with dopants of asecond polarity opposite the first polarity to form a doped layer in thesubstrate.

In one embodiment, the current confinement layer may be made frommaterial growth of Si, GeSi, Ge or a III-V material on the substrate.

In one embodiment, the absorption layer may be made from material growthof Si, GeSi, Ge or a III-V material on the current confinement layer.

In one embodiment, the device may be a normal incident photodiode or awaveguide photodiode.

In one embodiment, the device may be an edge-emitting laser or avertical cavity surface emitting laser (VCSEL).

In another aspect, a method of fabrication of a device may include:forming a current confinement layer on a substrate, the currentconfinement layer being doped in a pattern and configured to reduce darkcurrent in the device; forming an absorption layer on the currentconfinement layer; and forming an electrical contact layer on theabsorption layer and doped with dopants of a first polarity.

In one embodiment, forming the current confinement layer on thesubstrate may include doping the current confinement layer such that afirst portion of the current confinement layer with dopants of a secondpolarity opposite the first polarity.

In one embodiment, the first portion of the current confinement layermay be doped with dopants of the second polarity with a dopingconcentration from about 1×10¹⁶ to about 1×10²⁰/cm³.

In one embodiment, a second portion of the current confinement layersurrounding the first portion may be doped with dopants of the secondpolarity with a doping concentration has a doping concentration lessthan 1×10¹⁶/cm³.

In one embodiment, the method may further include etching a recess on afirst primary side of the substrate, where forming the currentconfinement layer on the substrate may include forming the currentconfinement layer on the first primary side of the substrate in therecess.

In one embodiment, the substrate may be made from a bulk Si wafer a SOIwafer.

In one embodiment, the method may further include doping a region on aside of the substrate on which the current confinement layer is disposedwith dopants of a second polarity opposite the first polarity to form adoped layer in the substrate.

In one embodiment, the method may form the current confinement layer onthe substrate by causing material growth of Si, GeSi, Ge or a III-Vmaterial on the substrate. In one embodiment, causing material growthmay include causing an epitaxial process by RPCVD, UHV/CVD or MOCVD.

In one embodiment, the method may form the absorption layer on thecurrent confinement layer by causing material growth of Si, GeSi, Ge ora III-V material on the current confinement layer. In one embodiment,causing material growth may include causing an epitaxial process byRPCVD, UHV/CVD or MOCVD.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments of the present disclosure and, together with thedescription, serve to explain the principles of the present disclosure.The drawings may not necessarily be in scale so as to better presentcertain features of the illustrated subject matter.

FIG. 1 is a structural diagram of a photodiode device with currentconfinement layer in accordance with an embodiment of the presentdisclosure.

FIG. 2 is a structural diagram of a photodiode device with currentconfinement layer in accordance with another embodiment of the presentdisclosure.

FIG. 3 is a structural diagram of a photodiode device with currentconfinement layer and patterned substrate in accordance with anembodiment of the present disclosure.

FIG. 4 is a structural diagram of a laser device with currentconfinement layer in accordance with an embodiment of the presentdisclosure.

FIG. 5 is a chart showing photodiode dark current with and without thecurrent confinement layer in accordance with another embodiment of thepresent disclosure.

FIG. 6 is a chart showing photodiode responsivity with and without thecurrent confinement layer in accordance with another embodiment of thepresent disclosure.

FIG. 7 is a structural diagram of a conventional photodiode device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overview

In conventional photodiode devices, the conductive currents that crossthe interface between the photonic device and substrate include at leastthe following: the current under the open area (optical sensitive areain photodiodes or photonic devices), the dark current under the blockedarea without photonic illumination, and the leakage currents fromsidewall. Not all of these currents have a positive contribution forphotonic devices: for example, for photodiode, the region where thelight is directly illuminated on (e.g., the central region) is usefulfor collecting optical signal and the rest parts are useless. The darkcurrent generated in blocked area and the leakage current from sidewalldo not have a positive contribution for photonic devices and, thus, needto be reduced or otherwise minimized significantly to improve thesignal-to-noise ratio of devices, e.g., Ge/Si photonic devices such asphotodiode, lasers and modulators. Accordingly, embodiments of astructure of the present disclosure include a current confinement layerthat aids the reduction of dark current.

Illustrative Examples

FIG. 1 illustrates a photodiode device 100 with current confinementlayer in accordance with an embodiment of the present disclosure.

As shown in FIG. 1, the photodiode device 100 includes a substrate 110,a current confinement layer 120 disposed on the substrate 110, anabsorption layer 130, which may be an intrinsic layer, disposed on thecurrent confinement layer 120, and an electrical contact layer 140disposed on the absorption layer 130 for electrical connection. One ormore electrical contacts 150 of a first polarity (e.g., p contacts),made of metal for example, may be disposed on the electrical contactlayer 140, which is doped with dopants of the first polarity. Thesubstrate 110 may be or made from, for example, a bulk silicon (Si)wafer or a silicon-on-insulator (SOI) wafer. The substrate 110 isheavily doped, and thus has a doped layer 115 doped with dopants of asecond polarity opposite the first polarity (e.g., n+ doped substratelayer) near its top surface on which the current confinement layer 120is disposed. One or more electrical contacts 160 of the second polarity(e.g., n++ contacts) may be located on the periphery of, and in contactwith, the doped layer 115 and the current confinement layer 120.

The current confinement layer 120 may be formed by, for example, growthof Si, GeSi, Ge or other III-V material on the substrate 110. Aftergrowth, the current confinement layer 120 is doped in a pattern. Forexample, a select portion in the current confinement layer 120 (e.g.,the central region thereof as shown in FIG. 1) is doped with higherconcentration than other portions of the current confinement layer 120(e.g., regions of the current confinement layer 120 surrounding thecentral region thereof). That is, the central region of the currentconfinement layer 120 may be doped while the regions surrounding thecentral region of the current confinement layer 120 may be intrinsicregions.

The absorption layer 130 is configured to collect optical signal, andmay be formed by, for example, growth of Si, GeSi, Ge or other III-Vmaterial on the current confinement layer 120.

Different from conventional designs such as that shown in FIG. 7, thephotodiode device 100 includes the current confinement layer 120 forreducing dark current. The current confinement layer 120 is notuniformly doped and has some pattern. As a result, most of theconductive currents will be confined to a region inside the heavilydoped region of the current confinement layer 120 because of resistancedifferences.

In one embodiment, the material growth may include epitaxial processesdone by reduced-pressure chemical vapor deposition (RPCVD), ultra-highvacuum chemical vapor deposition (UHV/CVD) or metal oxide chemical vapordeposition (MOCVD).

In one embodiment, the heavily doped region of the current confinementlayer 120 may have a doping concentration from about 1×10¹⁶ to about1×10²⁰/cm³. Moreover, the intrinsic regions of the current confinementlayer 120 may have a doping concentration has a doping concentrationless than 1×10¹⁶/cm³.

In one embodiment, the photodiode device 100 may be either a normalincident photodiode or a waveguide photodiode.

FIG. 2 illustrates a photodiode device 200 with current confinementlayer in accordance with another embodiment of the present disclosure.

As shown in FIG. 2, the photodiode device 200 includes a substrate 210,a current confinement layer 220 disposed on the substrate 210, anabsorption layer 230, which may be an intrinsic layer, disposed on thecurrent confinement layer 220, and an electrical contact layer 240disposed on the absorption layer 230 for electrical connection. One ormore electrical contacts 250 of the first polarity (e.g., p contacts),made of metal for example, may be disposed on the electrical contactlayer 240, which is doped with dopants of the first polarity. Thesubstrate 210 may be or made from, for example, a bulk Si wafer or a SOIwafer. The substrate 210 is etched first to form a recess 270 on the topside thereof, as shown in FIG. 2, and then heavily doped to form a dopedlayer 215 doped with dopants of the second polarity opposite the firstpolarity (e.g., n+ doped substrate layer) near its top surface on whichthe current confinement layer 220 is disposed. The recess 270 on the topside of the substrate 210 (i.e., the side of the substrate 110 on whichthe rest of the layers of the photodiode device 200 are disposed) allowsthe top surface, i.e., the electrical contact layer 240, to besubstantially or at least approximately flush with peripheral regions ofthe substrate 210 that are not recessed, such as where one or moreelectrical contacts 260 of the second polarity (e.g., n++ contacts) arelocated. The one or more electrical contacts 260 may be in contact withthe doped layer 215 of the substrate 210 but not in contact with thecurrent confinement layer 220.

The current confinement layer 220 may be formed by, for example, growthof Si, GeSi, Ge or other III-V material on the substrate 210. Aftergrowth, the current confinement layer 220 is doped in a pattern. Forexample, a select portion in the current confinement layer 220 (e.g.,the central region thereof as shown in FIG. 2) is doped with higherconcentration than other portions of the current confinement layer 220(e.g., regions of the current confinement layer 220 surrounding thecentral region thereof). That is, the central region of the currentconfinement layer 220 may be doped while the regions surrounding thecentral region of the current confinement layer 220 may be intrinsicregions.

The absorption layer 230 is configured to collect optical signal, andmay be formed by, for example, growth of Si, GeSi, Ge or other III-Vmaterial on the current confinement layer 220.

Different from conventional designs such as that shown in FIG. 7, thephotodiode device 200 includes the current confinement layer 220 forreducing dark current. The current confinement layer 220 is notuniformly doped and has some pattern. As a result, most of theconductive currents will be confined to a region inside the heavilydoped region of the current confinement layer 220 because of resistancedifferences.

In one embodiment, the material growth may include epitaxial processesdone by RPCVD, UHV/CVD or MOCVD.

In one embodiment, the heavily doped region of the current confinementlayer 220 may have a doping concentration from about 1×10¹⁶ to about1×10²⁰/cm³. Moreover, the intrinsic regions of the current confinementlayer 220 may have a doping concentration has a doping concentrationless than 1×10¹⁶/cm³.

In one embodiment, the photodiode device 200 may be either a normalincident photodiode or a waveguide photodiode.

FIG. 3 illustrates a photodiode device 300 with current confinementlayer and patterned substrate in accordance with an embodiment of thepresent disclosure.

As shown in FIG. 3, the photodiode device 300 includes a substrate 310,a current confinement layer 320 disposed on the substrate 310, anabsorption layer 330, which may be an intrinsic layer, disposed on thecurrent confinement layer 320, and an electrical contact layer 340disposed on the absorption layer 330 for electrical connection. One ormore electrical contacts 350 of the first polarity (e.g., p contacts),made of metal for example, may be disposed on the electrical contactlayer 340, which is doped with dopants of the first polarity. Thesubstrate 310 may be or made from, for example, a bulk Si wafer or a SOIwafer. The substrate 310 is heavily doped, and thus has a doped layer315 doped with dopants of the second polarity opposite the firstpolarity (e.g., n+ doped substrate layer) near its top surface on whichthe current confinement layer 320 is disposed. One or more electricalcontacts 360 of the second polarity (e.g., n++ contacts) may be locatedon the periphery of, and in contact with, the doped layer 315 and thecurrent confinement layer 320.

One major difference between the photodiode device 300 and thephotodiode device 100 is that the doping pattern of the doped layer 315of the substrate 310 is different from the doping pattern of the dopedlayer 115 of the substrate 110. For example, as shown in FIG. 3, thedoping layer 315 may be patterned such that the doping layer 315 has anon-uniform distribution of doping concentration in the area beneath thecurrent confinement layer 320.

The current confinement layer 320 may be formed by, for example, growthof Si, GeSi, Ge or other III-V material on the substrate 310. Aftergrowth, the current confinement layer 320 is doped in a pattern. Forexample, a select portion in the current confinement layer 320 (e.g.,the central region thereof as shown in FIG. 3) is doped with higherconcentration than other portions of the current confinement layer 320(e.g., regions of the current confinement layer 320 surrounding thecentral region thereof). That is, the central region of the currentconfinement layer 320 may be doped while the regions surrounding thecentral region of the current confinement layer 320 may be intrinsicregions.

The absorption layer 330 is configured to collect optical signal, andmay be formed by, for example, growth of Si, GeSi, Ge or other III-Vmaterial on the current confinement layer 320.

Different from conventional designs such as that shown in FIG. 7, thephotodiode device 300 includes the current confinement layer 320 forreducing dark current. The current confinement layer 320 is notuniformly doped and has some pattern. As a result, most of theconductive currents will be confined to a region inside the heavilydoped region of the current confinement layer 320 because of resistancedifferences.

In one embodiment, the material growth may include epitaxial processesdone by RPCVD, UHV/CVD or MOCVD.

In one embodiment, the heavily doped region of the current confinementlayer 320 may have a doping concentration from about 1×10¹⁶ to about1×10²⁰/cm³. Moreover, the intrinsic regions of the current confinementlayer 320 may have a doping concentration has a doping concentrationless than 1×10¹⁶/cm³.

In one embodiment, the photodiode device 300 may be either a normalincident photodiode or a waveguide photodiode.

As shown in FIG. 3, the dopant distribution of the doped layer 315 ofthe substrate 310 may be patterned. In one embodiment, the patterned anddoped substrate 310 may be formed by implantation on an intrinsicsubstrate, such as a bulk Si wafer or a SOI wafer, for example.

In one embodiment, the heavily doped region of the doped layer 315 thesubstrate 310 may have a doping concentration from 1×10¹⁶ to about1×10²⁰/cm³. Moreover, the intrinsic regions of the substrate 310 mayhave a doping concentration has a doping concentration less than1×10¹⁶/cm³.

FIG. 4 illustrates a laser device 400 with current confinement layer inaccordance with an embodiment of the present disclosure.

Other than photodiodes, the novel structure of the present disclosurecan be applied to laser for reducing threshold current, shown in FIG. 4.In one embodiment, the laser device 400 may be either an edge-emittinglaser or a vertical cavity surface emitting laser (VCSEL). That is, thelaser device 400 may be a laser device as well as a photodiode device.

As shown in FIG. 4, the laser device 400 includes a substrate 410, acurrent confinement layer 420 disposed on the substrate 410, an activelayer 430, which may be an intrinsic or heavily doped layer (e.g., n+doped), disposed on the current confinement layer 420, and an electricalcontact layer 440 disposed on the active layer 430 for electricalconnection. One or more electrical contacts 450 of the second polarity(e.g., n contacts), made of metal for example, may be disposed on theelectrical contact layer 440, which is doped with dopants of the secondpolarity. The substrate 410 may be or made from, for example, a bulk Siwafer or a SOI wafer. The substrate 410 is heavily doped, and thus has adoped layer 415 doped with dopants of the first polarity opposite thesecond polarity (e.g., p+ doped substrate layer) near its top surface onwhich the current confinement layer 420 is disposed. One or moreelectrical contacts 460 of the first polarity (e.g., p++ contacts) maybe located on the periphery of, and in contact with, the doped layer 415and the current confinement layer 420.

The current confinement layer 420 may be formed by, for example, growthof Si, GeSi, Ge or other III-V material on the substrate 410. Aftergrowth, the current confinement layer 420 is doped in a pattern. Forexample, a select portion in the current confinement layer 420 (e.g.,the central region thereof as shown in FIG. 4) is doped with higherconcentration than other portions of the current confinement layer 420(e.g., regions of the current confinement layer 420 surrounding thecentral region thereof). That is, the central region of the currentconfinement layer 420 may be doped while the regions surrounding thecentral region of the current confinement layer 420 may be intrinsicregions.

The active layer 430 is configured to generate light, and may be formedby, for example, growth of Si, GeSi, Ge or other III-V material on thecurrent confinement layer 420.

Different from conventional designs such as that shown in FIG. 7, thelaser device 400 includes the current confinement layer 420 for reducingthreshold current. The current confinement layer 420 is not uniformlydoped and has some pattern. As a result, most of the conductive currentswill be confined to a region inside the heavily doped region of thecurrent confinement layer 420 because of resistance differences.

In one embodiment, the material growth may include epitaxial processesdone by RPCVD, UHV/CVD or MOCVD.

In one embodiment, the heavily doped region of the current confinementlayer 420 may have a doping concentration from about 1×10¹⁶ to about1×10²⁰/cm³. Moreover, the intrinsic regions of the current confinementlayer 420 may have a doping concentration has a doping concentrationless than 1×10¹⁶/cm³.

In one embodiment, the laser device 400 may be either an edge-emittinglaser or a vertical cavity surface emitting laser (VCSEL).

FIG. 5 is a chart 500 showing photodiode dark current with and withoutthe current confinement layer in accordance with another embodiment ofthe present disclosure. FIG. 6 is a chart 600 showing photodioderesponsivity with and without the current confinement layer inaccordance with another embodiment of the present disclosure.

As shown in FIGS. 5 and 6, the novel structure of each of the photodiodedevice 100, the photodiode device 200, the photodiode device 300 and thelaser device 400, which includes a current confinement layer, reducesdark current without negatively impacting (e.g., causing loss of) theresponsivity of the device.

Additional Note

Although some embodiments are disclosed above, they are not intended tolimit the scope of the present disclosure. It will be apparent to thoseskilled in the art that various modifications and variations can be madeto the disclosed embodiments of the present disclosure without departingfrom the scope or spirit of the present disclosure. In view of theforegoing, the scope of the present disclosure shall be defined by thefollowing claims and their equivalents.

What is claimed is:
 1. A device, comprising: a substrate; a currentconfinement layer disposed on the substrate, the current confinementlayer being doped in a pattern and configured to reduce dark current inthe device; an absorption layer disposed on the current confinementlayer; and an electrical contact layer disposed on the absorption layerand doped with dopants of a first polarity.
 2. The device of claim 1,wherein a first portion of the current confinement layer is doped withdopants of a second polarity opposite the first polarity, and wherein asecond portion of the current confinement layer surrounding the firstportion comprises an intrinsic region.
 3. The device of claim 2, whereinthe first portion of the current confinement layer is doped with dopantsof the second polarity with a doping concentration from about 1×10¹⁶ toabout 1×10²⁰/cm³.
 4. The device of claim 2, wherein the second portionof the current confinement layer is doped with dopants of the secondpolarity with a doping concentration has a doping concentration lessthan 1×10¹⁶/cm³.
 5. The device of claim 1, wherein a first primary sideof the substrate includes a recess, and wherein the current confinementis disposed on the first primary side of the substrate in the recess. 6.The device of claim 5, wherein an exposed surface of the electricalcontact layer is approximately flush with a portion of the first primaryside of the substrate that is not recessed.
 7. The device of claim 1,wherein the substrate comprises a bulk Si wafer a silicon-on-insulator(SOI) wafer.
 8. The device of claim 1, wherein a region on a side of thesubstrate on which the current confinement layer is disposed is dopedwith dopants of a second polarity opposite the first polarity to form adoped layer in the substrate.
 9. The device of claim 1, wherein thecurrent confinement layer comprises material growth of Si, GeSi, Ge or aIII-V material on the substrate.
 10. The device of claim 1, wherein theabsorption layer comprises material growth of Si, GeSi, Ge or a III-Vmaterial on the current confinement layer.
 11. The device of claim 1,wherein the device comprises a normal incident photodiode or a waveguidephotodiode.
 12. The device of claim 1, wherein the device comprises anedge-emitting laser or a vertical cavity surface emitting laser (VCSEL).13. A method of fabrication of a device, comprising: forming a currentconfinement layer on a substrate, the current confinement layer beingdoped in a pattern and configured to reduce dark current in the device;forming an absorption layer on the current confinement layer; andforming an electrical contact layer on the absorption layer and dopedwith dopants of a first polarity.
 14. The method of claim 13, whereinforming the current confinement layer on the substrate comprises dopingthe current confinement layer such that a first portion of the currentconfinement layer with dopants of a second polarity opposite the firstpolarity.
 15. The method of claim 14, wherein the first portion of thecurrent confinement layer is doped with dopants of the second polaritywith a doping concentration from about 1×10¹⁶ to about 1×10²⁰/cm³. 16.The method of claim 14, wherein a second portion of the currentconfinement layer surrounding the first portion is doped with dopants ofthe second polarity with a doping concentration has a dopingconcentration less than 1×10¹⁶/cm³.
 17. The method of claim 13, furthercomprising: etching a recess on a first primary side of the substrate,wherein forming the current confinement layer on the substrate comprisesforming the current confinement layer on the first primary side of thesubstrate in the recess.
 18. The method of claim 13, wherein thesubstrate comprises a bulk Si wafer a silicon-on-insulator (SOI) wafer.19. The method of claim 13, further comprises doping a region on a sideof the substrate on which the current confinement layer is disposed withdopants of a second polarity opposite the first polarity to form a dopedlayer in the substrate.
 20. The method of claim 13, wherein forming thecurrent confinement layer on the substrate comprises causing materialgrowth of Si, GeSi, Ge or a III-V material on the substrate.
 21. Themethod of claim 20, wherein causing material growth comprises causing anepitaxial process by reduced-pressure chemical vapor deposition (RPCVD),ultra-high vacuum chemical vapor deposition (UHV/CVD) or metal oxidechemical vapor deposition (MOCVD).
 22. The method of claim 13, whereinforming the absorption layer on the current confinement layer comprisescausing material growth of Si, GeSi, Ge or a III-V material on thecurrent confinement layer.
 23. The method of claim 22, wherein causingmaterial growth comprises causing an epitaxial process byreduced-pressure chemical vapor deposition (RPCVD), ultra-high vacuumchemical vapor deposition (UHV/CVD) or metal oxide chemical vapordeposition (MOCVD).